ABY Splitter with isolated out

[bluelagoon]

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection.

taudio, I were advised that if you have the zener there for overvoltage protection, that it would also provide reverse polarity protection, which nul and voids the necessity for D1 Shotky

You could do that. However, there is a trade-off ...

Image you connect a 9 volt supply that is reverse polarity -- a likely case.

The Zener appears as a diode that drops ~0.7 volts. So, the 33 ohm resistor sees 9-0.7 = 8.3 volts

The power dissipation in the 33 ohm resistors will be V^2/R = 2W. So the resistor, which is likely 1/4W (unless you planned for this case) will burn up, becoming a fuse (and the pedal will no longer work).

If someone connects an 18 volt supply that is reverse polarity (less likely but possible), you need a 9W resistor to ensure it doesn't burn up. At some point, you'll also exceed the power dissipation of the Zener and it will also burn up -- this would happen much sooner if you don't have the resistor installed.

You could assume that the power supply that is connected in reverse polarity is current limited, which may save the resistor (and the diode), but this may not always be the case.

With the Schottky in place and a reverse supply connected, nothing happens -- at least up to the reverse breakdown voltage of the Schottky diode.

So, having both the Schottky and the Zener makes the design more robust ... and it only costs $0.20 extra

Okay thanks taudio, for that more broadly explained explanation, will know better in future. Cheers

[Mat88]

I've attached a better quality image showing only the Super Transformer power supply.

Hi taudio,
i'm not sure if i'm having a brain fart haha but...
i was looking at your power input with the TC1044SCPA.

I'm i understanding this all wrong or does your pedal don't work with the common pedal power center negative and needs a center positive pin to power it up?

That IC needs +V at the input right, the usual pedal dc cable for power is center negative -9v, but in your schematic it seems the pin 2 of the dc socket which is the tip of the connector is connected to the circuit, that's -9v there... I can see the battery + terminal is connected to the switched pin #3, thats fine when it disconnects the dc power cable, the battery engages but why is pin 2 of your dc socket seems to connect to the center -9v pin of the dc power cable?

It seems on this schematic from build your own clone website they wire it like i was thinking to make it, with the center pin connected to ground and sleeve connected to the diode and charge pump v+ input pin. That's reversing the usual power cable that's -9v center pin into a center pin positive +9v to feed the charge pump input pin.
https://byocelectronics.com/ampselectorschematic.pdf

[Mat88]

oh sheet, i was looking at it wrong...
Fist time i work with dc sockets like this.
The pin1 on your schematic is the center pin and pin2 is the outer sleeve, i got confused because 6.35mm sockets have the litle triangle thing to indicate the tip, i assumed the round shaped thing was the sleeve lol sorry
But then that's the build your own schematic that has it the wrong way...

[taudio]

oh sheet, i was looking at it wrong...
Fist time i work with dc sockets like this.
The pin1 on your schematic is the center pin and pin2 is the outer sleeve, i got confused because 6.35mm sockets have the litle triangle thing to indicate the tip, i assumed the round shaped thing was the sleeve lol sorry
But then that's the build your own schematic that has it the wrong way...

Yup -- you've got it. Here's the DC jack that I used.

I did find an embarrassing mistake in the schematic clip I sent. C10 has the polarity wrong. I'm now two for two on getting the capacitor polarity wrong

A corrected schematic is attached.

[Mat88]

oh sheet, i was looking at it wrong...
Fist time i work with dc sockets like this.
The pin1 on your schematic is the center pin and pin2 is the outer sleeve, i got confused because 6.35mm sockets have the litle triangle thing to indicate the tip, i assumed the round shaped thing was the sleeve lol sorry
But then that's the build your own schematic that has it the wrong way...

Yup -- you've got it. Here's the DC jack that I used.

I did find an embarrassing mistake in the schematic clip I sent. C10 has the polarity wrong. I'm now two for two on getting the capacitor polarity wrong

A corrected schematic is attached.

Thanks
Good catch!
And about the R10 51 ohm and C13 10n connected to ground at the output signal, what is the purpose?
There is similar on both designs from RG, but it's 10k and 1nf.

It's weird i dont get any email notification anymore from this thread even if i activate it

[FiveseveN]

center negative -9v

Please note the difference between ground and -9V. "Center negative" just means the ground is on the center pin.
From ground to 9V we have 9V.
From -9V to 9V we have 18V.

[antonis]

"Center negative" just means the ground is on the center pin.

Or the lower voltage level compared to outer pin..

[taudio]

oh sheet, i was looking at it wrong...
Fist time i work with dc sockets like this.
The pin1 on your schematic is the center pin and pin2 is the outer sleeve, i got confused because 6.35mm sockets have the litle triangle thing to indicate the tip, i assumed the round shaped thing was the sleeve lol sorry
But then that's the build your own schematic that has it the wrong way...

Yup -- you've got it. Here's the DC jack that I used.

I did find an embarrassing mistake in the schematic clip I sent. C10 has the polarity wrong. I'm now two for two on getting the capacitor polarity wrong

A corrected schematic is attached.

Thanks
Good catch!
And about the R10 51 ohm and C13 10n connected to ground at the output signal, what is the purpose?
There is similar on both designs from RG, but it's 10k and 1nf.

It's weird i dont get any email notification anymore from this thread even if i activate it

The 1nF and 10k on RG's design are connected across the transformer winding and are doing high frequency EQ (they are a "Zobel network"). Basically, as frequency increases, the capacitor eventually "disappears" and the transformer sees a 10k load which is the load it was designed for...

On my design I did some testing and found that if you are connected to a high impedance load (like the input of a guitar amp), having a 10k load in parallel all the time has a minimal impact on the high frequency response. I included a switch to disable this (internal) load so you can connect the output to a low impedance input (around 10k) because when driving a low impedance load, the high frequency response does roll off -- some test results are in the audioXpress article. If you don't need this, you can remove the switch.

Either approach (RG's EQ) or a 10k load should be fine but you should test to confirm.

The 51 ohm and 10 nF capacitor connected to ground are performing a different function. To gain ground isolation, we need to increase the impedance between the grounds, but in some cases if you make it too large (like the open circuit you will get if you don't connect them), you will get RFI pickup and other hum / buzz artifacts.

I used Jensen's app notes (a treasure trove of useful information)

https://www.jensen-transformers.com/application-notes/

and this discussion (with some "sound advice" from RG) to inform my design:

https://www.diystompboxes.com/smfforum/index.php?topic=109086.0

I hope this helps.

[Mat88]

The 1nF and 10k on RG's design are connected across the transformer winding and are doing high frequency EQ (they are a "Zobel network"). Basically, as frequency increases, the capacitor eventually "disappears" and the transformer sees a 10k load which is the load it was designed for...

On my design I did some testing and found that if you are connected to a high impedance load (like the input of a guitar amp), having a 10k load in parallel all the time has a minimal impact on the high frequency response. I included a switch to disable this (internal) load so you can connect the output to a low impedance input (around 10k) because when driving a low impedance load, the high frequency response does roll off -- some test results are in the audioXpress article. If you don't need this, you can remove the switch.

Either approach (RG's EQ) or a 10k load should be fine but you should test to confirm.

The 51 ohm and 10 nF capacitor connected to ground are performing a different function. To gain ground isolation, we need to increase the impedance between the grounds, but in some cases if you make it too large (like the open circuit you will get if you don't connect them), you will get RFI pickup and other hum / buzz artifacts.

I used Jensen's app notes (a treasure trove of useful information)

https://www.jensen-transformers.com/application-notes/

and this discussion (with some "sound advice" from RG) to inform my design:

https://www.diystompboxes.com/smfforum/index.php?topic=109086.0

I hope this helps.

Ah great thanks!
I was searching online without knowing it was a zobel and all i found was the common RC network for low pass lol

But why is the 10k gradually part of the transformer load as the freq increase and not at all frequencies? Is it just to smooth out the output impedance curve at high frequencies only? Since there is only a 10k on your design (no 1nf cap), it affects all frequencies equally compared to RG design?

Thanks i downloaded all pdf on that jensen page, will read the most i can but looking at RG design, this ground isolation isnt done like in your circuit. If i understand correctly... that means RG design completely isolate the grounds from the input to the output sockets while your circuit also isolates them but a little less to avoid the hum and buzz artifacts that can happen with complete ground isolation?

The link JFace added on post#7 in this thread you linked does not work:
https://www.diystompboxes.com/smfforum/index.php?topic=109086.0
was it this the same one?
https://www.jensen-transformers.com/wp-content/uploads/2014/08/ts_guide.pdf
I read that whole thread, many great information from RG there.


Thanks again, i really appreciate it

[Mat88]

Oh and correct me if i'm wrong but it looks like you are using the Ring of the "stereo" output socket on the top right of your schematic to make contact with the ground sleeve part of a normal TS guitar cable?

It looks that way to me and when nothing is connected to the output it's shorted to the ground lift switch (or not) with the r10 and c13.

What is the purpose of this? Is it to always get connexion from the transformer pin 4 to the sleeve of the output socket jack inserted?

The way i see it, there is the ring AND the sleeve pins connected to the actual sleeve of the jack inserted at the output 

[taudio]

Oh and correct me if i'm wrong but it looks like you are using the Ring of the "stereo" output socket on the top right of your schematic to make contact with the ground sleeve part of a normal TS guitar cable?

It looks that way to me and when nothing is connected to the output it's shorted to the ground lift switch (or not) with the r10 and c13.

What is the purpose of this? Is it to always get connexion from the transformer pin 4 to the sleeve of the output socket jack inserted?

The way i see it, there is the ring AND the sleeve pins connected to the actual sleeve of the jack inserted at the output 

I did that so you can optionally make the output balanced. When you plug a regular (not a TRS) cable into the output jack, it shorts the ring connection to "ground" (as determined by the ground lift switch). So, you get the transformer connected between "ground" and the tip. You get an unbalanced output.

If you plug in a TRS jack and short J5, the transformer winding will be connected between the tip and ring with the center tap connected to "ground" via J5 (again, as determined by the ground lift switch). You get a balanced output.

I'm guessing that you don't need a balanced output so you can just connect the transformer winding between the tip and sleeve connections.

[taudio]

The 1nF and 10k on RG's design are connected across the transformer winding and are doing high frequency EQ (they are a "Zobel network"). Basically, as frequency increases, the capacitor eventually "disappears" and the transformer sees a 10k load which is the load it was designed for...

On my design I did some testing and found that if you are connected to a high impedance load (like the input of a guitar amp), having a 10k load in parallel all the time has a minimal impact on the high frequency response. I included a switch to disable this (internal) load so you can connect the output to a low impedance input (around 10k) because when driving a low impedance load, the high frequency response does roll off -- some test results are in the audioXpress article. If you don't need this, you can remove the switch.

Either approach (RG's EQ) or a 10k load should be fine but you should test to confirm.

The 51 ohm and 10 nF capacitor connected to ground are performing a different function. To gain ground isolation, we need to increase the impedance between the grounds, but in some cases if you make it too large (like the open circuit you will get if you don't connect them), you will get RFI pickup and other hum / buzz artifacts.

I used Jensen's app notes (a treasure trove of useful information)

https://www.jensen-transformers.com/application-notes/

and this discussion (with some "sound advice" from RG) to inform my design:

https://www.diystompboxes.com/smfforum/index.php?topic=109086.0

I hope this helps.

Ah great thanks!
I was searching online without knowing it was a zobel and all i found was the common RC network for low pass lol

But why is the 10k gradually part of the transformer load as the freq increase and not at all frequencies? Is it just to smooth out the output impedance curve at high frequencies only? Since there is only a 10k on your design (no 1nf cap), it affects all frequencies equally compared to RG design?

Thanks i downloaded all pdf on that jensen page, will read the most i can but looking at RG design, this ground isolation isnt done like in your circuit. If i understand correctly... that means RG design completely isolate the grounds from the input to the output sockets while your circuit also isolates them but a little less to avoid the hum and buzz artifacts that can happen with complete ground isolation?

The link JFace added on post#7 in this thread you linked does not work:
https://www.diystompboxes.com/smfforum/index.php?topic=109086.0
was it this the same one?
https://www.jensen-transformers.com/wp-content/uploads/2014/08/ts_guide.pdf
I read that whole thread, many great information from RG there.

Thanks again, i really appreciate it

Using the RC network versus the 10K resistor across the transformer secondary is a design choice that is usually determined via testing -- take a look at the frequency response (and possibly the transient response) of the transformer output into the loads you're likely to see in the "real world" (e.g., the input of a guitar amp). So, I recommend that you do testing (and listening) to see what works best for you.

In early versions of the Super Transformer I used a 600:600 ohm transformer and I didn't get hum and buzz; however, when I moved to a 10k:10k transformer, it appeared. So, it is transformer dependent and is related to the resistance / impedance to ground in the secondary winding. Some research I did confirmed that you don't need to disconnect the grounds, you just need to increase the impedance between them enough.

The Jensen schematic that inspired the grounding approach used on the Super Transformer is this one. I figured if it was good enough for Jensen (who are experts at this sort of thing), it was good enough for me You could experiment with this and see what works best for you (or make it switchable with a SPDT on-off-on switch).

Re: the links

- the first one works for me ("Hum problem with transformer isolated guitar splitter").

- the second one gives a good overview of the perils and challenges faced in grounding. This one is also good (I read it as part of my research mentioned above).

Good luck!

[Mat88]

Oh and correct me if i'm wrong but it looks like you are using the Ring of the "stereo" output socket on the top right of your schematic to make contact with the ground sleeve part of a normal TS guitar cable?

It looks that way to me and when nothing is connected to the output it's shorted to the ground lift switch (or not) with the r10 and c13.

What is the purpose of this? Is it to always get connexion from the transformer pin 4 to the sleeve of the output socket jack inserted?

The way i see it, there is the ring AND the sleeve pins connected to the actual sleeve of the jack inserted at the output 

I did that so you can optionally make the output balanced. When you plug a regular (not a TRS) cable into the output jack, it shorts the ring connection to "ground" (as determined by the ground lift switch). So, you get the transformer connected between "ground" and the tip. You get an unbalanced output.

If you plug in a TRS jack and short J5, the transformer winding will be connected between the tip and ring with the center tap connected to "ground" via J5 (again, as determined by the ground lift switch). You get a balanced output.

I'm guessing that you don't need a balanced output so you can just connect the transformer winding between the tip and sleeve connections.

Ah ok yeah, makes sense thanks

[Mat88]

The 1nF and 10k on RG's design are connected across the transformer winding and are doing high frequency EQ (they are a "Zobel network"). Basically, as frequency increases, the capacitor eventually "disappears" and the transformer sees a 10k load which is the load it was designed for...

On my design I did some testing and found that if you are connected to a high impedance load (like the input of a guitar amp), having a 10k load in parallel all the time has a minimal impact on the high frequency response. I included a switch to disable this (internal) load so you can connect the output to a low impedance input (around 10k) because when driving a low impedance load, the high frequency response does roll off -- some test results are in the audioXpress article. If you don't need this, you can remove the switch.

Either approach (RG's EQ) or a 10k load should be fine but you should test to confirm.

The 51 ohm and 10 nF capacitor connected to ground are performing a different function. To gain ground isolation, we need to increase the impedance between the grounds, but in some cases if you make it too large (like the open circuit you will get if you don't connect them), you will get RFI pickup and other hum / buzz artifacts.

I used Jensen's app notes (a treasure trove of useful information)

https://www.jensen-transformers.com/application-notes/

and this discussion (with some "sound advice" from RG) to inform my design:

https://www.diystompboxes.com/smfforum/index.php?topic=109086.0

I hope this helps.

Ah great thanks!
I was searching online without knowing it was a zobel and all i found was the common RC network for low pass lol

But why is the 10k gradually part of the transformer load as the freq increase and not at all frequencies? Is it just to smooth out the output impedance curve at high frequencies only? Since there is only a 10k on your design (no 1nf cap), it affects all frequencies equally compared to RG design?

Thanks i downloaded all pdf on that jensen page, will read the most i can but looking at RG design, this ground isolation isnt done like in your circuit. If i understand correctly... that means RG design completely isolate the grounds from the input to the output sockets while your circuit also isolates them but a little less to avoid the hum and buzz artifacts that can happen with complete ground isolation?

The link JFace added on post#7 in this thread you linked does not work:
https://www.diystompboxes.com/smfforum/index.php?topic=109086.0
was it this the same one?
https://www.jensen-transformers.com/wp-content/uploads/2014/08/ts_guide.pdf
I read that whole thread, many great information from RG there.

Thanks again, i really appreciate it

Using the RC network versus the 10K resistor across the transformer secondary is a design choice that is usually determined via testing -- take a look at the frequency response (and possibly the transient response) of the transformer output into the loads you're likely to see in the "real world" (e.g., the input of a guitar amp). So, I recommend that you do testing (and listening) to see what works best for you.

In early versions of the Super Transformer I used a 600:600 ohm transformer and I didn't get hum and buzz; however, when I moved to a 10k:10k transformer, it appeared. So, it is transformer dependent and is related to the resistance / impedance to ground in the secondary winding. Some research I did confirmed that you don't need to disconnect the grounds, you just need to increase the impedance between them enough.

The Jensen schematic that inspired the grounding approach used on the Super Transformer is this one. I figured if it was good enough for Jensen (who are experts at this sort of thing), it was good enough for me You could experiment with this and see what works best for you (or make it switchable with a SPDT on-off-on switch).

Re: the links

- the first one works for me ("Hum problem with transformer isolated guitar splitter").

- the second one gives a good overview of the perils and challenges faced in grounding. This one is also good (I read it as part of my research mentioned above).

Good luck!

Thanks so much for all the links and details about your design.
I will start to prototype something now and see how it goes

[Mat88]

Hm just to make sure, i'm i the only one not being able to access https://geofex.com/ ?

[Mat88]

Oh i almost forgot about this...
On the radial aby there's no ground plane around the DC socket.
Any ideas they did that? Another ground isolation somehow?

[taudio]

Hm just to make sure, i'm i the only one not being able to access https://geofex.com/ ?

I can't access it with link in your message.

However, I can enter it into my browser and access it.

[Mat88]

Hm just to make sure, i'm i the only one not being able to access https://geofex.com/ ?

I can't access it with link in your message.

However, I can enter it into my browser and access it.

Oh i was trying to access it through google search or when posted here in the comments of RG and it did not work but now i understand, it's not HTTPS, only HTTP. I can access it by typing it without HTTPS, thanks

[PRR]

not being able to access https://geofex.com/ ?

Take out the "s" in https. (Your browser may be "helpfully" putting it in.)  http://geofex.com/

Like Clapton's first guitar or Ringo's first snare, R.G.'s website is very historical, and lacks some modern "frills". No, the lack of the "s" does not make it insecure (its not your bank).

[Mat88]

not being able to access https://geofex.com/ ?

Take out the "s" in https. (Your browser may be "helpfully" putting it in.)  http://geofex.com/

Like Clapton's first guitar or Ringo's first snare, R.G.'s website is very historical, and lacks some modern "frills". No, the lack of the "s" does not make it insecure (its not your bank).

Oh yeah thanks i know but i just didnt see it at first since it's been a while i went to a site that's not https.
btw if RG see this comment, look at openssl, it's free ssl certificate for websites and most hosts can set it up for you.